First-come, first-served (FCFS) – sometimes first-in, first-served and first-come, first choice – is a service policy whereby the requests of customers or clients are attended to in the order that they arrived, without other biases or preferences. Those who wait for the event or service in line may stand in a queue. The policy can be employed when processing sales orders, in determining restaurantseating, on a taxi stand, etc. In Western society it is the standard policy for the processing of most queues in which people wait for a service that was not prearranged or booked in advance.

The practice is also common among some airlines that don't issue seat reservations. These airlines board passengers in small groups based upon order of check-in, and the passengers choose their own seats. The earlier passengers check in, the earlier they board the aircraft to choose a seat. Passengers are sequentially (on a first-come, first-served basis) assigned into one of several "boarding groups."

Scheduled services and events often use a different service policy. A restaurant may take reservations in advance and reserve a table so they can seat the party when they arrive at the designated time.

The phrase is often (but erroneously) stated as "first come, first serve" (instead of "served"). This is an error because "come" is grammatically functioning as a past participle, as it does in the sentence: "They have come." The phrase abbreviates the sentence "The first to have come is the first to be served."